Enlarged Sink Capacity and Optimized Population Physiological Characteristics are Key to High Yield in Conventional Japonica Rice

Clarifying the photosynthetic and population characteristics of conventional japonica rice at different yield levels is crucial for boosting yield and ensuring food security. Therefore, a two-year field trial with two conventional japonica varieties was conducted at four planting densities: 16 cm × 30 cm (D1), 14 cm × 30 cm (D2), 12 cm × 30 cm (D3), and 10 cm × 30 cm (D4). This study aimed to investigate how photosynthetic and population characteristics influence grain yield under varying planting densities. The results indicated that higher yields were primarily driven by increased grain weight and seed-setting rate (with a 9.68%‒11.40% higher single panicle weight), supported by optimized dry matter translocation and source-sink relationships. Elevated planting density (D2‒D4) enhanced panicle number and total spikelet number (by 3.91%‒15.00%) but reduced the number of spikelets per panicle, 1000-grain weight, and photosynthetic efficiency due to mutual shading. Despite these trade-offs, yield increased by 4.10%‒12.42% under higher densities. The use of planting density D4 in japonica rice cultivation contributed to maximize yield. These findings provide important theoretical insights and practical significance for increasing the yield of conventional japonica rice and ensuring food security.